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Visualizing a huge amount of complex models can be a time consuming part of the rendering process. For many complex objects specialized methods exist. This seminartopic is about the realtime visualization of forests.
Rendering forests can be a time consuimg task making it hard to find a method that is capable of rendering many trees in real time while maintining a decent visual quality. To achieve interactive framerates many methods introduce simplifications that lead to so called popping artifacts that distract the user and lower the immersion.

In recent years many advances and the development of modern graphics hardware lead to more elaborated methods which are capable of processing and rendering millions of trees in real time and with popping artifacts and convincing lighting effects.

The gradient of a scalar function is a well-known tool of vector analysis and routinely used to analyze images or results of simulations or to enhance volume visualization. In these applications, the gradient is usually not known but has to be approximated from the values of the function which are commonly given on a discrete set of points in some space. If these points lie on a regular, orthogonal grid, approximation of the gradient can be easily done using divided differences. In the case of non-orthogonal meshes, this is not as simple. In this seminar, several methods will be presented which can overcome this problem.

The computation of geodesic paths and distances on triangle meshes is a common operation in many computer graphics applications. I will present several practical algorithms for computing such geodesics from a source point to one or all other points efficiently.
First, I will describe an implementation of the exact “single source, all destination” algorithm presented by Mitchell, Mount, and Papadimitriou (MMP). I will show that the algorithm runs much faster in practice than suggested by worst case analysis.
I will also show an algorithm (by V. And T. Surazhsky, D. Kirsanov, Steven J. Gortler and H. Hoppe) extended with a merging operation to obtain computationally efficient and accurate approximations with bounded error.
Finally, to compute the shortest path between two given points, I will show how the authors used a lower-bound property of their approximate geodesic algorithm to efficiently prune the frontier of the MMP algorithm, thereby obtaining an exact solution even more quickly.

The rendering of realistic scenes in real time is an important goal of computer graphics. For a scene to appear realistic, the shadowing of the scene has to seem correct. There are several techniques to render real time shadows and Shadow Mapping is one of the most prominent of those. Many extensions of this technique have been developed to increase the quality of the resulting Shadows. This talk will give an overview of one of these extensions, the Convolution Shadow Mapping, which allows for better filtering of the shadows and thus increasing the image quality.

In computer graphics and especially in virtual reality it is not only important to represent rigid objects, but also to simulate deformable materials. Curves, surfaces, or solids should deform according to interaction with other objects and react in a natural way. A wide variety of techniques have been developed for modeling and animation of deformable objects. One possible approach is to model the underlying physics by solving differential equations that balance externally applied forces with the object’s inertial mass as well as the damping force and an elastic force resulting from deformation. The computation of the required deformation energy is derived from differential geometry and can be simplified for real-time simulation. In this work the elastically deformable models are distinguished from other techniques and the basic equations and computations are described.

Segmentation is a problem in many areas of research and application. Therefore many different approaches exist to find regions of interest in images. A widely used approach employs so-called "Atlases" to which the image of interest is mapped.
This seminar will give an overview of the technique and describe a general non-rigid registration technique and similarity measure which are used to find the mapping between atlas and image.

A family of discrete isometric bending models (IBMs) for triangulated surfaces in 3-space will be presented. It will be shown that these linear models for discrete mean curvature from which bending energies are assembled are very efficient. Under the assumption of isometric surface deformations it is also shown the formulated energies are quadratic in surface positions. The corresponding linear energy gradients and constant energy Hessians constitute an efficient model for computing bending forces and their derivatives, enabling fast time-integration of cloth dynamics with a two- to three-fold net speedup over existing nonlinear methods.

The Medial Axis is an important geometric concept related to the Voronoi diagram and other distance-sets. Even though its definition is easily stated and intuitive, the computation of the Medial Axis for non-trivial sets is difficult and time-consuming. The computation of the Voronoi diagram in contrast is well understood and there exist stable algorithms. This is the first of two talks presenting the approximation of the Medial Axis from the Voronoi diagram.

The Medial Axis is an important geometric concept related to the Voronoi diagram and other distance-sets. Even though its definition is easily stated and intuitive, the computation of the Medial Axis for non-trivial sets is difficult and time-consuming. The computation of the Voronoi diagram in contrast is well understood and there exist stable algorithms. This is the first of two talks presenting the approximation of the Medial Axis from the Voronoi diagram.

Traditionally, research on computer graphics is centered around the quest for visual realism. But looking at even older techniques of illustration one notices that there is a need for non-photorealistic drawings, for example in the area of medical imaging and for educational purposes. Here an image should display the relevant features of an object rather than rendering it photorealistically.
We present a method to (semi-)automatically generate such representations from a given polygonal model of the object. The technique is based on calculating lines of intersection along a skeleton of the object model.

In the last twenty years many approaches for contact-free measurement techniques for object surfaces and approaches for 3d object reconstruction have been proposed; but often they still require complex and expensive equipment. Not least due to the rapidly increasing number of efficient 3d hard- and software system components, alternative low-cost solutions are in great demand. We propose such a low-cost system for 3d data acquisition and fast pairwise surface registration. The only hardware requirements are a simple commercial hand-held laser and a standard grayscale camera.

Spherical Harmonic lighting (SH lighting) is a technique for calculating the lighting on 3D models from area light sources that allows us to capture, relight and display global illumination style images in real time. The talk gives an overview of this technique starting from the definition of global illumination to the interreflectance between objects.

Resampling raw surface meshes is one of the most fundamental operations used by nearly all digital geometry processing systems. The vast majority of this work has focused on triangular remeshing, yet quadrilateral meshes are preferred for many surface PDE problems, especially fluid dynamics, and are best suited for defining Catmull-Clark subdivision surfaces.
We describe a fundamentally new approach to the quadrangulation of manifold polygon meshes using Laplacian eigenfunctions, the natural harmonics of the surface. These surface functions distribute their extrema evenly across a mesh, which connect via gradient flow into a quadrangular base mesh.
An iterative relaxation algorithm simultaneously refines this initial complex to produce a globally smooth parameterization of the surface. From this, we can construct a well-shaped quadrilateral mesh with very few extraordinary vertices.The quality of this mesh relies on the initial choice of eigenfunction, for which we describe algorithms and heuristics to efficiently and effectively select the harmonic most appropriate for the intended application.

Shape from Shading (SFS) deals with the recovery of shape from a gradual variation of shading in an image. This is particularly important in applications where direct surface measurements are not possible. The basic problems of SFS and three different approaches for a solution are presented in the seminar.

Cloth modeling has been an important topic studied by computer graphics people since the mid of 1980s. Beside the visual pleasantness of a fabric, the hand or feel of the fabric plays an important role in the perception of a fabric.

Roughness and friction are important parameters for the haptic simulation of fabrics. In this talk a DFFT based correlation-restoration method to model the surface roughness and friction coefficient of a given fabric is described.